Connection promoted by annual floods shaping the response community attributes of shallow lakes fish inhabit the upper Paraná River floodplain

The temporal variability of the hydrological cycle plays a key role in shaping the diversity of the biotic components in floodplains. However, species respond differently to this cycle, and therefore, lakes can function as natural laboratories to test hypotheses about the interactions between the mechanisms involved in this dynamic. Here, we evaluate whether and how the level of the Paraná River affects the structure of fish assemblages in the littoral region of lakes (with and without permanent connection to the Paraná River), using taxonomic richness and species similarity data from a time series of 14 years. Our main working hypothesis was that the ecological descriptors (species richness, abundance, and spatial vs. temporal distribution) of fish assemblages, among lakes with different degrees of connection to the main river of the floodplain, may respond differently to the variation in the hydrological level. The results showed a significant difference in the composition of fish assemblages among the studied lakes, but the trends depended on the year considered (2002, 2006, 2012, and 2013). Therefore, despite of the artificial regulation promoted by dams upstream, the hydrological cycle still is the main driver of beta-diversity in littoral fish assemblages from shallow lakes in this floodplain. In addition, the variability of the composition of these assemblages is also straightly dependent on the features of the floods. Our results highlight the importance of seasonal variability in the hydrological level of this river for non-stochastic assembly rules of fish communities across spatial and temporal scales.